NGC 4194

This article is about a pair of interacting galaxies. For the Medusa planetary nebula, see Medusa Nebula.

NGC 4194, the Medusa merger, is a galaxy merger in the constellation Ursa Major about 128 million light-years (39.1 Mpc) away.^[4] It was discovered on April 2, 1791 by German-British astronomer William Herschel.^[8] Due to its disturbed appearance, it is object 160 in Halton Arp's 1966 Atlas of Peculiar Galaxies.^[7]

A black hole in Medusa's tail

NGC 4194
Observation data (J2000 epoch)
Constellation	Ursa Major
Right ascension	12h 14m 09.64s[1]
Declination	+54° 31′ 34.60″[1]
Redshift	0.008433[2]
Heliocentric radial velocity	2,511±12 km/s[3]
Distance	128 Mly (39.1 Mpc)[4]
Apparent magnitude (V)	13.30[5]
Apparent magnitude (B)	13.79[5]
Characteristics
Type	Imeger[2]
Apparent size (V)	0.14′ × 0.13′[6]
Notable features	Interacting, starburst
Other designations
Medusa galaxy merger, NGC 4194, Arp 160, UGC 7241, Mrk 201, PGC 39068[7]

The morphological classification of NGC 4194 is Imeger,^[2] indicating an irregular form. This galaxy consists of a brighter central region spanning an angular size 9″ across, with an accompanying system of loops and arcs. Additional material is thinly spread out to a radius of 75″ from the central region.^[9] There is a tidal tail and regions undergoing high levels of star formation, making this a starburst galaxy. It is a source for strong infrared and radio emission.^[10][11] These features indicate NGC 4194 is a late-stage galaxy merger.^[12] A region of extreme star formation 500 ly (150 pc) across exists in the center of the Eye of Medusa, the central gas-rich region.^[13]

Within 1.2 kpc (3.9 kly) of the dynamic center of NGC 4194, star formation is occurring at a rate of 8 M_☉·yr⁻¹. The star forming regions in this volume range from 5 to 9 million years in age, with the youngest occurring in areas of the highest star formation rate.^[14] As of 2014, no galactic nucleus has been detected based on radio emissions, nor have the respective nuclei of the merger galaxies.^[15] However, X-ray emission from a black hole in the tidal tail was detected by Chandra in 2009.^[16]